The present invention relates to a thin film magnet head which is to be guided over a recording medium to be magnetized perpendicularly in which flux changes are to be registered along a track with predetermined record wavelength and flux change density, and which contains a flux-carrying head-like guiding element with two magnet legs. These magnet legs constitute magnet poles facing the recording medium which are arranged one behind the other seen in the direction of relative movement of the magnet head with respect to the recording medium, spaced by a gap of predetermined width, and which have predetermined extents in the direction of movement, and outside the region of the magnet poles they define an interstice through which extend the turns of at least one write and/or read coil winding. Such a magnet head is shown, e.g. in EP-A-No. 0 012 912.
The principle of perpendicular magnetization for storage of data in appropriate recording media is generally known (cf. e.g. "IEEE Transactions on Magnetics", Vol. MAG-16, No. 1, January, 1980, pages 71 to 76, or Vol. MAG-20, No. 5, September, 1984, pages 657 to 662 and 675 to 680). The recording media to be provided for use with this principle, often referred to as vertical magnetization or vertical data storage, may be present in particular in the form of rigid magnetic memory plates. Such a recording medium has at least one memory layer of predetermined thickness, to be magnetized accordingly, made of a material with vertical magnetic anisotropy, the axis of the so-called easy magnetization of this layer being oriented perpendicular to the surface of the recording medium. Preferred as a memory material is CoCr (cf., e.g., "IEEE Transactions on Magnetics", Vol. MAG-14, No. 5, September, 1978, pages 849 to 851). By means of special magnet heads, the individual data can then be registered along a track as bits in successive sections by appropriate remagnetization of the memory layer in the form of flux changes. The bits or flux changes have a predetermined extent in the longitudinal direction of the track, referred to also as record wavelength. This extent may be substantially smaller for vertical magnetization than for storage according to the known principle of longitudinal (horizontal) magnetization, where reduction of the record wavelength is limited by the demagnetization of the material. That is, by perpendicular magnetization, the data density can be increased as compared with longitudinal magnetization.
Now if one guides a thin film magnet head of the initially mentioned kind along a track over a record medium in which magnetic flux changes have been registered by vertical magnetization, a predetermined read voltage can be produced with this head. This read voltage depends on the number of flux changes per unit length of the track, i.e., on the flux change density. A corresponding curve of the read voltage as a function of this flux change density in a diagram is known as a roll-off curve. Now it is found that with known thin film magnet heads this curve assumes for a certain value of the flux change density a marked maximum value D.sub.p and drops sharply with further increase of the flux change density (cf., e.g., "IEEE Transactions on Magnetics", Vol. MAG-23, No. 1, January, 1987, pages 177-179). This decrease of the read voltage can be explained by a superposition (interference) of the bipolar read signals--progressing with increasing flux change density--which one obtains when reading a single flux change.
Because of this marked dependence of the read voltage on the flux change density, in particular in the range of the maximum value D.sub.p, the expense for signal processing in a read/write channel of the magnet head of the initially mentioned kind is correspondingly great.